My 2010 Expedition has 287000 miles. Without any codes, I change the Earl ☺️and service it regularly. I've owned it about 2 years. I drive it 1500 miles a couple of times a year. It is also my daily driver. On these 1500 mile trips which take me about 24 hours round trip, the fuel economy increases from 10 mpg to 15 mpg by the time I get home. It only happens on that trip. Why and can I duplicate this every day.  She runs good and is very responsive. It runs for about 3 hours before the economy start to creep up 10.1, 10.3, 10.7 so on and so for the trip. By the time I pull into my driveway it's at 15.1. A few days later she's back to 10 mpg, why? I would just like to see it daily.